SERT Inhibitors, including the selective serotonin transporter inhibitors, also called selective serotonin reuptake inhibitors (SSRI's), have become the most frequently prescribed antidepressant drugs. They are believed to exert their effect by increasing extracellular 5-HT levels in the serotoninergic terminal fields such as the hippocampus and prefrontal cortex. However, approximately 30% of patients appear to be resistant to SSRI treatment. In addition, those patients who do benefit from SSRI treatment often exhibit various side-effects which include sexual dysfunction, gastrointestinal distress, insomnia and in some cases anxiogenesis due to their indirect activation (through elevation of 5-HT levels) of all 5-HT receptors.
Furthermore, a common problem in current antidepressant therapies is their slow onset of action, since a delay of about 4 weeks is normally observed between the beginning of the treatment and alleviation of the symptoms. The delay appears to parallel the progressive desensitization of somatodendritic 5HT1A receptors, increasing serotoninergic function, thus allowing alleviation of depressive symptoms.
Recent reports have indicated that the combination of a SSRI and a NK-1 antagonist produces beneficial responses in animal models of anxiety and depression such as guinea-pig pup maternal separation vocalization, with relatively reduced doses (WO98/47514;. Bioorg. Med. Chem. Lett. 12(2), 261-264 (2002) and Bioorg. Med. Chem. Lett. 12(21), 3195-3198 (2002).
This suggests that by adopting a dual approach which is mechanistically dissimilar, a synergism between the two modes of action may occur, enabling enhanced responses. This may not only be beneficial in patients resistant to treatment with SSRI alone but also in improving the rapidity of onset of therapeutic action. A drug with a dual mode of action potentially allows for a reduction in dosing and therefore a decreased risk of side effects as compared to a combination of two drugs.
In the patent literature the combined NK-1I/SSRI approach has also been proposed as a potential treatment for obesity (WO98/47514). WO2005/032464 describes trans-phenyl pyrrolidine ethers, which are tachykinin receptor antagonists.